A version of this article appears in print on May 22, 2015, on page A13 of the New York edition with the headline: Scientists Find Tiny Additions to the Tree of Life. photo : Christian Sardet/Centre National de la Recherche Scientifique/Tara Expéditions

Climate change scientists have known for years that rising temperatures affect sea creatures, from the biggest fish to the microscopic plankton at the base of the ocean food chain. Now, a four-year expedition that sampled microbes from across the world’s oceans is bringing the mechanisms of that change into focus.

These tiny creatures, which may be among the oldest on Earth, together absorb carbon dioxide, make oxygen, break down waste and nourish other creatures. And they are profoundly affected by water temperature, according to a series of five studies published Thursday in Science about the voyage of the schooner Tara.

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